all sites that use flashplayer play video but the sound will not come on

i'm having the same problem... i have a quad G5 (PPC) with OS X.4.8 , flash
doesn't work either in Safari or Firefox and on both of the users registered on
the computer...
i was just on the phone with AppleCare, tried several things but at the end
couldn't help me because it's an Adobe product...
is there an incompatibilty after the apple software update?
this is what i have in my internet plug-ins folder:
AdobePDFViewer.plugin
DRM Plugin.bundle
Flash Player.plugin
flashplayer.xpt
Flip4Mac WMV Plugin.plugin
Flip4Mac WMV Plugin.webplugin
iPhotoPhotocast.plugin
Java Applet Plugin Enabler
Java Applet.plugin
JavaPluginCocoa.bundle
NP-PPC-Dir-Shockwave
nsIQTScriptablePlugin.xpt
Quartz Composer.webplugin
QuickTime Plugin.plugin
QuickTime Plugin.webplugin
RealPlayer Plugin.plugin
VerifiedDownloadPlugin.plugin
does anyone have an idea? thx for the help